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cs2204: unit 7: Discussion Assignment

Simultaneous TCP connection initiations are rare, but simultaneous connection termination is relatively common. How do two TCP nodes negotiate the simultaneous sending of FIN packets to one another? Draw the ladder diagram, and label the states on each side. Which node goes into TIMEWAIT state?

  • let’s start by explaining the normal circumstances; in which the host who wishes to close the connection sends its FIN packet and enters the active close path; while the other end will enter the passive close path.
  • the active close path, starts from ESTABLISHED state; then this host sends its FIN packet, call it FIN1, and enters FIN_WAIT_1; upon receiving the other end’s ACK of FIN1, this host enters the FIN_WAIT_2 state where it waits for any data that is left to be sent from the other end; once the other end finishes sending data it sends its own FIN, call it FIN2, then this host enters the TIMEWAIT state; after that, it will send the ACK of FIN2 and enters the CLOSED state.
  • the other host starts the closing process by receiving the FIN1 signal where its state changes to CLOSE_WAIT; then it sends all the data to the other end; the sends its own FIN, we called it FIN2, and enters the LAST_ACK state where it waits for the ACK of FIN2; and then enters the CLOSED state.

tcp close

  • so in the normal circumstances, the host who wishes to end the connection enters the TIMEWAIT state; but the newer versions of TCP, requires the client to always initialize the closing routine, since this will save the server from having to save the connection connection data, to make sure the same client can not use the same port very soon.

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